Piezoelectric igniter



Dec. 23, 1969 L. STEINKE T AL PIEZO'ELEGTRIC IGNITER P max 300 kp ai s F-IG.3

FIGA

INVENTQRS Leo ST E|NKE,Gerhc|rd SOHNER Kurt HURST, Richard GERBER I Parl F'RlMMEL,Otto HERRMANN WMIJW their ATTORNEY United States Patent Int. (:1. rzs a/oo, 5/00 U.S. Cl. 317-81 13 Claims ABSTRACT OF THE DISCLOSURE A piezoelectric igniter wherein a striking member is propelled against one of two parallel-connected piezoelectric elements with a predetermined force to produce a potential difference of first polarity between two electrodes which define a spark gap resulting in the discharge of at least one primary spark across and ionization in the spark gap. When the blow upon the one piezoelectric element is terminated, the resulting change in the mechanical stress produces a potential difference of opposite polarity to bring about one or more secondary discharges across the ionized spark gap. If a hard-to-ignite gas is not ignited by a primary spark, it is ignited by the secondary discharge.

BACKGROUND OF THE INVENTION The present invention relates to improvements in piezoelectric igniters, particularly to improvements in igniters which may be utilized for ignition of gaseous fuels. Still more particularly, the invention relates to igniters which can be used to ignitiate combustion of hard-toignite gases, especially city gas, butane, natural gas and/ or others.

In certain presently known piezoelectric igniters, the blow transmitted to a piezoelectric elment causes a change in the mechanical stress which effects the discharge of a single spark across a spark gap. The spark produced by the blow is of short duration and does not always suffice to insure ignition of certain types of gaseous fuels, for example, butane or natural gas. Therefore, such igniters are normally employed for ignition of readily combustible gases, particularly pressurized gaseous lighter fuel. Reference may be had to U.S. Patent No. 3,200,295 which discloses a lighter for ignition of pressurized gaseous lighter fuel by piezoelectric means.

It is also known to provide a piezoelectric igniter with a pressure transmitting lever which can transmit static stresses in the range of 300-500 ps. Such igniters which are disclosed, for example, in German DAS 1,218,216 are not entirely satisfactory because they are too bulky for many applications and because the manually applied pressure varies within a wide range. If the user applies a pressure which is too weak, the electrical energy is wasted due to internal resistance of the electric circuit and the igniter fails to produce a spark. If the pressure is excessive, the piezoelectric elements are likely to be destroyed.

SUMMARY OF THE INVENTION It is an object of our invention to provide a simple, compact and reliable piezoelectric igniter wherein the piezoelectric element or elements are subjected to identical stresses in response to each of a series of successive actuations of the igniter and which is capable of igniting all or nearly all types of combustible gases including those which are much more difficult to ignite than pressurized gaseous lighter fluid or the like.

Another object of the invention is to provide the igniter with a striking device which invariably transmits to the piezoelectric means blows of identical magnitude and which takes advantage of the reversibility of the piezoelectric effect to insure that the generation of sparks proceeds during a relatively long interval of time which is ample to effect ignition of butane, natural gas or similar hard-to-ignite gaseous fuels.

The improved piezoelectric igniter comprises means forming a spark gap; piezoelectric means including at least one piezoelectric element, electrodes electrically connected with the piezoelectric means and with the sides of the spark gap, striking means having a predetermined mass and movable toward and away from the piezoelectric means, and biasing means arranged to propel the striking means toward the piezoelectric means with a force exactly tuned to the mass of the striking means so that the striking means imparts to the piezoelectric means a blow of predetermined magnitude to cause a sudden first change in the mechanical stress therein resulting in potential difference of first polarity between the sides of the spark gap and in the discharge of at least one primary spark across and an ionization of the spark gap. The first change in the mechanical stress is thereupon followed by a gradual second change in response to termination of the blow and results in a potential difference of opposite polarity to effect at least one secondary discharge across the ionized spark gap. If the primary spark or sparks fail to ignite a hard-to-ignite gaseous fuel, the secondary discharge suffice to effect ignition even of very hard-to-burn gases, such as city gas, butane, natural gas and/or others.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved piezoelectric igniter itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of a specific embodiment with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial sectional view of a piezoelectric igniter which embodies our invention, the striking means being shown in starting position;

FIG. 2 is a partly elevational and partly axial sectional view of the housing in the piezoelectric igniter, the striking means being shown in blow-transmitting position;

FIG. 3 is a diagram showing the manner in which the mechanical stresses in the piezoelectric elements vary during and subsequent to transmission of a blow; and

FIG. 4 is a diagram showing the manner in which the potential difference at the electrode varies during and subsequent to transmission of a blow.

DESCRIPTION OF THE PREFERRED EMBODIMENT The piezoelectric igniter of FIGS. 1 and 2 comprises a tubular housing 10 which is open at one end and comprises an end wall 10a at the other end. The housing 10 is grounded and accommodates a cylindrical anvil 11 abutting against an elastic cushion 12 which is adjacent to the inner side of the end wall 10a. That surface of the anvil 11 which faces away from the end wall 10a is provided with a cylindrical recess 11a for the lower end portion of an insulating sleeve 13 which surrounds two stacked piezoelectric elements 14 of cylindrical shape. The elements 14 are connected in parallel and their opposite poles are adjacent to each other. These poles are connected with a central electrode which extends from the housing 10 through a radial nipple 13b of the sleeve 13. The latter is further provided with an external projection or collar 13a which is fitted into the housing 10. This collar 13a forms part of anchoring means for the sleeve 13, and such anchoring means further includes one, two or more internal projections of lugs 1012 provided in the housing 10 and a spring 16 which is inserted between the projections 10b and collar 13a to bias the sleeve 13 against the anvil 11 and to thus prevent recoiling or rebounding of the sleeve when the upper piezoelec' tric element 14 receives a blow. The upper portion of the sleeve 13 is surrounded by a helical return spring 17 which operates between the collar 13a and an internal surface of a cupped striking member 18. The latter is reciprocable in the housing 10 toward and away from the upper piezoelectric element 14. The striking member 18 has a lower end surface which is provided with a recess serving to accommodate a portion of the return spring 17. The upper end portion of the striking member 18 is of reduced diameter and is provided with a flange 19 which can be engaged by the lower end portions 26 of elastic claws 20 installed in the upper part of the housing 10. In addition, the flange 19 serves as an abutment for the lowermost convolution of a helical spring 21 which constitutes a biasing means and serves to propel the striking member 18 against the upper piezoelectric element 14 when the lower end portions 26 of the claws 20 are disengaged from the flange 19 by the lower end face of a cylindrical actuating member or knob 22 which is reciprocable in a mounting ring 24 connected with the upper end portions of claws 20 and held in the top part of the housing 10 by a nut 25 which meshes with an externally threaded portion of the housing. The knob 22 has two, three or more equidistant radially outwardly extending arms 22a which are slidable along the internal surface of the housing 10. A guide pin or post 23 of the striking member 18 extends upwardly beyond the flange 19 and is surrounded by the c nvolutions of the spring 21. This post 23 serves as a guide for the knob 22 when the latter is depressed to stress the spring 21 and to move its lower end face 22b into engagement with suitably configurated cams 27 pr vided on the claws 20 directly above the respective lower end portions 26. The claws 20 yield in response to downward movement of the knob 22, and their disengagement from the flange 19 takes place upon requisite stressing of the spring 21 so that the latter overcomes the resistance of the return spring 17 and propels the striking member 18 against the upper piezoelectric element 14. The retaining means including the claws 20 and mounting ring 24 preferably consists of suitable synthetic thermoplastic material.

FIG. 1 shows the striking member 18 in a starting position in which the surface at the upper end of the recess in this striking member is remote from the upper piezoelectric element 14. The arms 22a of the knob 22 passes through two of the claws 20.

The operation is as follows:

In order to ignite a combustible gaseous fuel, the operator applies finger pressure against the upper end of the knob 22 so as to move the arms 22a along the internal surfaces of the housing 10 and to stress the spring 21. The lower end face 22b of the knob 22 engages the cams 27 when the spring 21 stores sufficient energy, and further depression of the knob causes the end portions 26 of the claws 20 to move away from the flange 19 so that the spring 21 is free to dissipate energy and to propel the striking member 18 against the upper piezoelectric element 14. The striking member imparts to this element 14 a blow of predetermined magnitude to cause a first change in the mechanical stress in the piezoelectric elements 14. The spring 21 is much stronger than and can readily overcome the opposition of the return spring 17 when the knob 22 is depressed to the extent necessary to disengage the claws 20 from the flange 19 of the striking member 18. The operator then releases the knob 22 so that the spring 17 is free to expand and to return the striking member 18 to the starting position shown in FIG. 1. The faces of the end portions 26 of claws 20 are inclined downwardly and outwardly in order to permit upward movement of the flange 19 so that this flange is reengaged by the claws and is held in the starting position. The expanding return spring 17 need not overcome the resistance of the spring 21 because the operator removes his or her finger from the knob 22 as soon as the claws 20 release the flange 19. FIGS. 1 and 2 show that the flange 19 resembles a short frustrum of a cone and tapers upwardly to facilitate its passage along the lower faces of the end portions 26 and back to the starting position.

In the embodiment shown in FIGS. 1 and 2, the mass of the striking member 18 is about 45 grams, and the mass of the anvil 11 is greater, preferably about twice the mass of the striking member. The mass of the striking member 18 and the characteristics of the spring 21 are tuned to each other in such a way that the mechanical stresses in the piezoelectric elements 14 change substantially or exactly in a manner as shown in FIG. 3 while and immediately after the striking member 18 imparts a blow in response to disengagement of its flange 19 from the claws 20. The maximum mechanical stress (P is about 300 kp. and the stress rises substantially in the same way as the no-load potential difference between the sides of the piezoelectric elements 14 with a maximum of about 17 kv. The sides 28a, 28b of a spark gap 28 are respectively connected with the electrode 15 and with the ground. The housing 10 constitutes a second electrode which is electrically connected with the side 28b and with the two outer poles of the piezoelectric elements 14. The striking member 18 is metallic and is in current-conducting contact with the grounded housing 10. When the striking member 18 imparts a.

blow, the thus released electrical energy rises suddenly in a manner as shown in FIG. 4 during an initial interval of about 3 microseconds to cause the discharge of one or more primary sparks across the spark gap 28 and to cause ionization of the spark gap. The maximum potential dilference (U for this discharge between the sides 28a, 28b is about 15 kv. The potential difference collapses suddenly when a spark discharge occurs (see FIG. 4).

A gradual second change in mechanical stressing of the piezoelectric elements 14 occurs on termination of the blow. Such second change is the reduction of mechanical stress and produces a potential difference of opposite polarity as shown in FIG. 4. This second potential difference causes an arc discharge or secondary discharge across the ionized spark gap 28, and such secondary discharge is terminated after an interval of about 7 microseconds following the primary discharge. Thus, the entire ignition process takes up an interval of at least ten microseconds. Readily combustible gases are ignited in response to one or more primary discharges. City gas, butane or like gases which are not readily combustible are normally ignited in response to secondary discharge across the spark gap 28.

The duration of secondary discharge can be extended for one or several microseconds by placing the spark gap forming means in series with a suitable resistor 29, e.g., an ohmic resistor and/ or an inductive resistor. For example, the resistor 29 may constitute a conventional anti-interference cable of the type often employed in internal combustion engines. Such cable may have an inductance of 5-50 microhenry an an ohmic resistance of 530 kiloohms.

Our invention is based on the recognition that certain hard-to-ignite gases can be ignited if they are brought into contact with an arc discharge of relatively long duration and if such discharge generates a certain minimum amount of heat energy. This is achieved by relating the mass of the striking member and the bias of the spring 21 to each other in such a way that there develops a sudden rise in mechanical stress upon the piezoelectric elements 14 when the striking member imparts a blow so that the rise in mechanical stress suffices to produce a primary spark and to cause ionization of the spark gap 28. When the mechanical stress decreases upon termination of the blow, the resulting potential difference suflices to cause one or more secondary discharges across the ionized spark gap. The total interval of discharge is thus extended to at least ten microseconds in order to insure the ignition of nearly all types of gaseous fuels.

The utilization of the resistor 29 is of particular advantage if the piezoelectric means comprises two parallel-connected piezoelectric elements which double the amount of electrical energy that develops in response to transmission of a blow and subsequent to termination of the blow. The manner in which the spark gap 28 can be placed adjacent to a main gas line or a pilot line is known and forms no part of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications Without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A piezoelectric igniter, particularly for ignition of combustible gases, comprising, in combination, electrode means forming a spark gap; a housing; piezoelectric means located in said housing and including at least one piezoelectric element electrically connected in circuit with said electrode means; striking means in said housing and having a predetermined mass and being movable toward and away from said piezoelectric means for striking the same and thereby causing electric current to flow to said electrode means, creating an electric spark in said spark gap for igniting said combustible gases; biassing means arranged to propel said striking means towards said piezoelectric means; an anvil in said housing adjacent to said piezoelectric means opposite to said striking means and having a mass greater than that of said striking means; and elastic cushioning means interposed between said anvil and said housing opposite said piezoelectric means.

2. An igniter as defined in claim 1, wherein the mass of said anvil is about twice the mass of said striking means.

3. An igniter as defined in claim 1, wherein said housing is of tubular shape and comprises an end wall, wherein said anvil is of cylindrical shape and is slidably guided in said housing, and wherein said cushioning means comprises a rubber plate sandwiched between said anvil and said end wall of said housing, said anvil abutting with the end thereof opposite said piezoelectric means against said plate.

4. An igniter as defined in claim 3, wherein said anvil is provided with a recess accommodating at least a portion of said piezoelectric means.

5. An igniter as defined in claim 3, further comprising surrounding said piezoelectric means in said housing, and anchoring means for guiding and retaining the sleeve in said housing.

6. An igniter as defined in claim 5, said anchoring means comprising an external projection provided on said sleeve and slidably fitted into said housing, at least one internal projection provided on said housing and spring means operating between said projections to bias said sleeve against said anvil.

7. An igniter as defined in claim 1, wherein said striking means comprises a flange and including retaining means comprising elastic claw means engaging said flange for yieldably holding said striking means in a starting position remote from said piezoelectric means.

8. An igniter as defined in claim 7, further comprising actuating means movable in said housing to stress said biasing means and to thereupon disengage said flange from said claw means so that the biasing means is free to propel the striking means against said piezoelectric means.

9. An igniter as defined in claim 8, wherein said biasing means comprises a helical spring interposed between said flange and said actuating means, said striking means having a guide pin surrounded by said helical spring.

10. An igniter as defined in claim 8, wherein said claw means comprises a plurality of equidistant claws having end portions engageable with said flange.

11. An igniter as defined in claim 8, wherein said claw means comprises a plurality of claws having first end portions engageable with said flange and second end portions, and mounting means connected with said second end portions and fixed to said housing.

12. An igniter as defined in claim 8, wherein said claw means comprises a plurality of elastic claws having end portions engaging said flange in starting position of said striking means and cams adjacent to such end portions and engageable by said actuating means to disconnect said end portions from said flange.

13. An igniter as defined in claim 8, wherein said actuating means comprises outwardly extending arms slidable along the internal surface of said housing.

References Cited UNITED STATES PATENTS 3,200,295 8/1965 Owens et al 431-255 X 3,324,317 6/1967 Hazelst 310-87 X 3,344,314 9/1967 Koontz 31781 3,384,786 5/1968 Oyamada et al 31781 3,387,912 6/1968 Goto 317-81 X 3,408,153 10/1968 Ishiguro 3l781 X FOREIGN PATENTS 1,386,718 12/1964 France.

VOLODYMYR Y. MAYEWSKY, Primary Examiner US. Cl. X.R. 3l0-8.7; 317-96; 43l-255 

